Key Points

Compared with never smokers, smoking at the time of a breast cancer diagnosis was associated with a 69% increased risk of all-cause mortality.

The risk of all-cause mortality was elevated 130% among women who continued smoking after diagnosis compared with never smokers. Although the risk of all-cause mortality remained elevated among women who quit smoking after diagnosis, the increase in the risk of mortality was estimated at 83% compared with never smokers.

Breast cancer survivors may benefit from aggressive smoking cessation programs starting as early as the time of diagnosis.

According to the American Cancer Society, about 316,120 new cases of breast cancer will be diagnosed this year, and over 40,000 women will die of the disease. Between 10% and 20% of women diagnosed with cancer are current smokers. Now, a prospective study by Parada et al investigating whether at-diagnosis smoking and postdiagnosis changes in smoking habits within 5 years after breast cancer were associated with long-term all-cause and breast cancer–specific mortality finds that compared with never smokers, smoking at the time of diagnosis was associated with a 69% increased risk of all-cause mortality. Breast cancer survivors may benefit from aggressive smoking cessation programs starting as early as the time of diagnosis. The study was published in JNCI Cancer Spectrum.

Study Methodology

The researchers analyzed data from 1,508 participants in the Long Island Breast Cancer Study Project, a population-based study of newly diagnosed patients with breast cancer, who were diagnosed with first primary in situ or invasive breast cancer in 1996 to 1997. The women were interviewed about their lifestyle, including smoking habits, shortly after their diagnosis and again approximately 5 years later to assess their smoking history. They were followed for vital status through December 2014. After 18+ years of follow-up, 597 deaths were identified, 237 of which were related to breast cancer. Mutivariable Cox regression was used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs).

The study participants were primarily white (94%), with a mean age of 59 years, and postmenopausal (68%) at the time of diagnosis.

Study Results

The researchers found that compared with never smokers, the risk of all-cause mortality was elevated among the 19% of at-diagnosis smokers (HR = 1.69, 95% CI = 1.36–2.11), those who smoked 20 or more cigarettes per day (HR = 1.85, 95% CI = 1.42–2.40), women who had smoked for 30 or more years (HR = 1.62, 95% CI = 1.28–2.05), and women who had smoked 30 or more pack-years (HR = 1.82, 95% CI = 1.39–2.37). Risk of all-cause mortality was further increased among the 8% of women who were at-/postdiagnosis smokers (HR = 2.30, 95% CI = 1.56–3.39) but was attenuated among the 11% of women who quit smoking after diagnosis (HR = 1.83, 95% CI = 1.32–2.52). Compared with never smokers, breast cancer–specific mortality risk was elevated 60% (HR = 1.60, 95% CI = 0.79–3.23) among at-/postdiagnosis current smokers, but the confidence interval included the null value and elevated 175% (HR = 2.75, 95% CI = 1.26–5.99) when the researchers considered postdiagnosis cumulative pack-years.

Quitting Smoking May Improve Survival

“Smoking negatively impacts long-term survival after breast cancer. Post-diagnosis cessation of smoking may reduce the risk of all-cause mortality. Breast cancer survivors may benefit from aggressive smoking cessation programs starting as early as the time of diagnosis,” concluded the study authors.